The invention relates to antennas and antenna feed systems and more particularly to a system in which a one electrical wavelength closed loop is voltage fed and matched to a low impedance feed line.
In order to transfer energy between a feed line and an antenna, typically some means is required to match or transform the antenna feed point impedance to the feed line characteristic impedance. Ideally, the matched antenna feed point should present a resistive, non-reactive impedance equal to the feed line characteristic impedance. Traditionally, most antennas having yagi type or loop type (the latter often referred to as "quad" antennas if square or diamond configured loops or as a "delta loop" if triangularly configured) have been fed by electrically opening the driven element so as to provide a current feed to a relatively low impedance point in conjunction with one of various types of matching devices (i.e., gamma match, stub match, inductive match, hairpin match, etc.). However, voltage feed for such antennas has not been popular due largely to the problems resulting from the requirement to handle high voltage (often in difficult environmental conditions) and the requirement to match the high impedance feed point to a relatively low impedance feed line.
Generally, voltage feed has been employed mainly in connection with antenna systems in which current feed is not reasonably possible, such as in feeding a long wire antenna.
In one prior art antenna system devised by the present inventor voltage feed to a one wavelength loop type antenna was achieved by means of a parallel resonant LC (inductor-capacitor) circuit having its high impedance point connected to the loop and being fed from a low impedance transmission line by means of an inductive link coupling to the resonant circuit inductor. The system was found to be susceptible to high voltage damage and was found to be difficult to adequately weatherproof.